> I have a coupla questions... First, why does it only display a center cut
> rectangle of the full image. Why when I put it in a Render in Image node does
> it sort of work, but then comes off its wheels and starts displaying random
> noise? (It does show the full image when I feed the Render In Image node into
> a Billboard).
It only displays the center because the GLSL Grid's size is too big -- it
should be 2 wide at most, and it looks to be 3 and a fraction. The Width and
Height inputs control this, so you can see which patches control this (Image
Dimensions, I think)
Render In Image probably needs a clear patch. If that doesn't help, please
post a sample composition that shows the problem you're encountering.
> Last but not least... How does it work? I've looked at the code and it seems
> so simple. The Fragment code just feeds all pixels out to the Vertex code and
> it does some tiny magic, and then boom, there it is.
GPUs have been built to interpolate values between corners (Normals, Colors,
texture coordinates) -- they do this extraordinarily well. This shader takes
advantage of that -- it's basically "free" (no math required on your part)
because of the way GPUs work.
Also, the fragment doesn't go to the vertex - it's the other way around:
Vertex Shaders operate on the vertices supplied (possibly changing them, and
setting up data for the fragment shader), and then the fragment shader runs for
each pixel defined by the (possibly changed) vertices. There are typically
many many more fragments ("pixels", but not always) than there are vertices, so
vertex-shader-supplied data is interpolated across the fragments by the GPU.
You happened to want data interpolated in that manner, which made it pretty
simple. :) _______________________________________________
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